1. Technical Field
The present disclosure pertains to control devices of discharge lamps and to related systems and methods.
2. Description of the Related Art
Fluorescent lamps typically comprise a glass tube which contains a small quantity of mercury, a low pressure inert gas and phosphorous powders which coat the inside part of the tube. At the extremities two electrodes are present which, connected to a suitable driving circuit, form an arc that permits the discharge of the gas to be generated and maintained.
Among the possible driving circuits the so-called high frequency ballast circuits can be enumerated: these are circuits at output of which an alternating voltage signal is generated at a frequency and amplitude necessary to keep the lamp on; this waveform is produced by a circuit that comprises a couple of transistors driven by an oscillator and which switch at a frequency of tens of KHz, a current limiting coil or choke and a filtering capacitance.
The prior art generally controls the maximum current/voltage of lamp, formed with a closed loop system with limited bandwidth.
US 2008290809 discloses a driving circuit comprising an half bridge and an oscillator adapted to determine the switching frequency of the half bridge. The control circuit comprises regulating means adapted to regulate the value of the switching frequency when the value of the voltage across the lamp exceeds a prefixed value.
Therefore, in the event of a choke saturation, the system reacts to the over current Ic increasing the frequency of the oscillator by an amount proportional to the single over current on more periods.